Weird Linker Error

[AldenB]

I was going back through Principles and Programming by Stroustrup and after completing the chapter 6 exercise I was left with these weird linker errors with very unhelpful messages (to me). Does anyone know what's wrong here?

/* error LNK2019: unresolved external symbol "public: __thiscall Token_stream::Token_stream(void)" (??0Token_stream@@QAE@XZ) referenced in function "void __cdecl `dynamic initializer for 'ts''(void)" (??__Ets@@YAXXZ) */

/* error LNK1120: 1 unresolved externals */

Source code:

#include "std_lib_facilities.h";

class Token
{
public:
	char kind;
	double value;
};
class Token_stream
{
public:
	Token_stream();
	void putback(Token t);
	Token get();
private:
	bool full{ false };
	Token buffer;
};

void Token_stream::putback(Token t)
{
	if (full) error("putback() into full buffer.");
	buffer = t;
	full = true;
}
Token Token_stream::get()
{
	if (full)
	{
		full = false;
		return buffer;
	}
	char ch;
	cin >> ch;

	switch (ch)
	{
	case ';':
	case 'q':
	case '(': case ')': case '+': case '-': case '*': case '/':
		return Token{ ch };
	case '.':
	case '0': case '1': case '2': case '3': case '4':
	case '5': case '6': case '7': case '8': case '9':
	{
		cin.putback(ch);
		double val;
		cin >> val;
		return Token{ '8', val };
	}
	default: error("Bad token");
	}
}

Token_stream ts;
double expression();

double primary()
{
	Token t = ts.get();
	switch(t.kind)
	{
	case '(':
	{
		double d = expression();
		t = ts.get();
		if (t.kind != ')')error("')' expected");
		return d;
	}
	default: error("primary expected");
	}
}
double term()
{
	double left = primary();
	Token t = ts.get();

	while (true)
	{
		switch (t.kind)
		{
		case '*': left *= primary();
			t = ts.get();
			break;
		case '/':
		{
			double d = primary();
			if (d == 0) error("divide by zero");
			left /= d;
			t = ts.get();
			break;
		}
		default:
			ts.putback(t);
			return left;
		}
	}
}
double expression()
{
	double left = term();
	Token t = ts.get();

	while (true)
	{
		switch (t.kind)
		{
		case '+': left += term();
			t = ts.get();
			break;
		case '-': left -= term();
			t = ts.get();
			break;
		default:
			ts.putback(t);
			return left;

		}
	}
}

int main()
{
	try
	{
		double val{ 0 };
		while (cin)
		{
			Token t = ts.get();

			if (t.kind == 'q') break;
			if (t.kind == ';') cout << "=" << val << endl;
			else ts.putback(t);
			val = expression();
		}
	}
	catch (exception& e)
	{
		cerr << e.what() << endl;
		keep_window_open();
		return 1;
	}
	catch (...)
	{
		cerr << "exception" << endl;
		keep_window_open();
		return 2;
	}
}

[drew887]

The error message is saying that you never defined the body for the Token_stream class' constructor. It looks like you don't really need a constructor for the class any way so you could just use a default constructor.

class Token_stream
{
public:
	Token_stream(); // try removing or commenting out this line and see if that fixes things
	void putback(Token t);
	Token get();

[AldenB]

You're awesome it worked perfectly! Thank you so much. I can't believe I didnt consider that before.